The present invention relates to an oscillator employing a piezoelectric vibrator in which it is easy to control the oscillation frequency and to keep the oscillation frequency constant over a wide temperature range.
For example, in a crystal oscillator, a trimmer condenser is needed to control the oscillation frequency, and therefore the oscillator construction becomes complex. Also, the oscillation frequency drifts according to changes in the temperature, so the oscillator can be used only in a narrow temperature range. Even in an oscillator having a minimum frequency drifting rate, its oscillation frequency drifts about .+-.2 PPM in the temperature range 5.degree. to 35.degree. C., and out of this temperature range, the oscillation frequency drifts considerably.